# select user();
# select database();
# select now();

# select * from 表名;
# select 字段名 from 表名;
# select 字段名,字段名,字段名 from 表名;

# select distinct 字段 from 表;
    # 对查出来的字段进行去重

# select emp_name,salary*12 from 表
    # 字段salary参与了四则运算

# select concat(字段,'字符串2',字段) from 表
# select concat(emp_name,' : ',salary) as info from employee;
# select concat(emp_name,' : ',salary) info from employee;
# select concat_ws('分隔符',字符串,字段1,字段2) info from employee;
# select concat_ws('|','信息',emp_name,salary) info from employee;

# select(
#     case
#     when emp_name = 'alex' then
#         concat(emp_name,'BIGSB')
#     when emp_name = 'jingliyang' then
#         emp_name
#     else
#         concat(emp_name,'sb')
#     end
#     ) as new_name
# from employee;

